Melt blowing is a process for manufacturing nonwoven products by extruding molten thermoplastic resin through fine capillary holes (orifices) and blowing hot air on each side of the extruded fibers to attenuate and draw down the fibers. The fibers are collected on a screen or other suitable collection device as a random entangled nonwoven web. The web may be withdrawn and further processed into consumer goods such as mats, fabrics, webbing, filters, battery separators, and the like.
Because of the extreme precision required in machining the orifices and flow passages, a key portion of the die, frequently referred to as the die tip, is separately manufactured using high quality steel. The die tip is then assembled into the die body.
The die tip is an elongate member having a nose piece of triangular cross section. The orifices are drilled in the tip of the triangular apex and communicate with an internal flow channel formed in the die tip.
A serious problem associated with die tips of this construction is the reduced mechanical strength in the apex region of the die tip. The orifices, in combination with the internal flow channel, creates a weakness in the apex region of the structure because of the reduced cross sectional area of steel in this region. The high internal pressures caused by extruding the molten resin through the tiny orifices frequently causes the nosepiece to fail in tension at the apex. This problem was identified in U.S. Pat. No. 4,486,161 which teaches the use of integral tie bars spanning the die tip flow channel. This reference also discloses (FIG. 2) the use of bolts and spacers across the flow channel.